I have the setting show in the simple product as the image shown in the link below. BUT when i changed the product to ‘Product Type: Variable product' i do not see the same shipping option. I would be appreciate it, if you could shed some light on this.

Hello Michael,
Variable Product is an Advanced Feature of WooCommerce. Suppose you offer a same design t-shirt in different colors and the different colors cost differently and ship from different areas and shipping charges are different as well; for that purpose, you'll use variable product.
More Details on variable product can be found here http://docs.woothemes.com/document/product-variations/

So that's why the shipping tab is being hidden and instead of the shipping tab, you get the variations tab. To use the variations, you must select the attribute first and then you'll be able to select the variations and shipping charges.

as you mention in the previous reply. ‘you’ll be able to select the variations and shipping charges.' as i seen in my setting seller could only select the shipping class but can't define the shipping cost by themselves. If know the shipping class it define by myself in the woocommerce, in this case mean the seller couldn't have the flexibility to fill with their own shipping cost other than choose from the shipping class that i pre-define?

I found dokan shipping setting do provide with the shipping cost for per seller/ per item. From what i tested, if i change it to per seller dokan will take the highest shipping amount set in per item (If this setting can be taking care by the seller themselves will be great. Instead of taking higher amount they set in per item maybe they can have a field to fill up the standard shipping).

per item will only based on 1 qty. how if the seller like to based on quantity to increase the shipping cost?

I'm a developer, but i'm not familiar with wordpress. I know i could make some changed in the child theme by using ‘hook' . but i do not have any idea on how to use that yet. Also i'm confusing should i make any changes on the plugin, even thought in the child theme. Will it causing the update fail if any?